The warning light indicates insufficient battery charge. Use a battery tester to see whether the alternator is giving a good charge i.e. 12-13v+. If it is below the aforementioned, your alternator is not charging the battery sufficiently. If you haven't got a tested, go to Halfords to get them to check the battery (the battery could be defective even when new) and the alternator.
If the earthstrap is defective, you will have instances where the engine will not start due to no electricity supply. When you turn the ignition, there is no clicking sound. This was what happened to mine.